This is just 50km south of Kyushu — Japan’s most southerly main island.

The dome itself is 9.5km wide. The seabed has been forced upwards some 610 meters by more than 31 cubic kilometers of lava.

“The lava dome is chemically different from the super-eruption, suggesting that a new magma supply system had been developed after 7,300 years ago,” Tatsumi told The New York Times.

This means the super volcano has found a new and different source of magma.

“The post-caldera activity is regarded as the preparation stage to the next super-eruption,” Tatsumi told Live Science, “not as the calming-down stage from the previous super-eruption.”

Lava at the surface of the central dome. The surface of lava dome consists of rhyolite blocks with water-chilled, tortoiseshell contraction cracks (b) and pillow lobe structures. A photograph (a) was supplied from NHK.

Amid the evidence for this are active hydrothermal springs and dense streams of gas bubbling up from the sea bed.

But evidence of life is not evidence of an impending mega eruption.

LOOKING AHEAD

The lava dome is a sign. But not a portent of doom.

But if it was to burst, the resulting eruption of steam and gas would have a serious effect on the global climate. Temperatures would plunge by several degrees. Crops would fail. The weather would go wild.

Exactly how far down the track of this terrible fate Kikai has travelled is hoped to be determined next month.

A new survey involving seismic and electromagnetic sensors will combine with underwater robots to clarify exactly what shape the caldera is in — and thereby hopefully exposing what forces are at play.

Researchers also hope to form a picture of the underground magma reservoir to a depth of 30km.

Based on these results, they hope to refine expectations for when the next eruption is due.

Its peak sits just 30m beneath the ocean waves.

But the dome is not in itself a problem.

It’s what it represents.

It means a vastly bigger crucible of magma below has begun building up pressure once again.

If it bursts, researchers say it could kill some 100 million people.

HISTORIC TERROR

Kikai has exploded before. Japanese volcanologists have found ample evidence of an eruption of 500 cubic kilometers of magma some 7000 years ago.

There is evidence of another super-eruption about 95,000 years ago. And another some 140,000 years.

Where it’s at now, volcanologist Yoshiyuki Tatsumi says there is about a 1 per cent chance of a “catastrophic” eruption within 100 years.

Three surveys have conducted sonar, submersible and seismic mapping of the site to get a picture of what is going on down below.